Regarding determining EI with large format negatives:(posted 8237 days ago)I found this site (sorry, URL has long since been lost) which described a great way to determine EI and save film at the same time.
Take a thin piece of cardboard (I used mat board) and cut it so it fits inside the frame of your film holder. Then, cut a series of rectangular openings. On a 4x5 negative, I cut out three rows of five. Three rows of four are probably better. Save the cutouts. Then, take some thinner cardboard (the cardboard inside film packages works great) and cut them into rectangles that are just a bit bigger than the first set of cutouts. Glue the thinner pieces onto the smaller pieces.
You'll probably want to mark the original cutouts so you know which hole they go back into. Orientation is important as well for a good fit.
Once you've created the 'plugs', here's what you do:
1. Tape the card board cutout into the opening of your film holder. You'll have to load film first :-) Keep the dark slide in place.
2. Point your camera at an evenly lit wall, and take the camera slightly out of focus. You don't want detail.
2. Set your film speed for 1/2 the recommended ISO, and meter the wall. Close down by four stops to get a zone I exposure. Then, remove the first plug, remove the dark slide, and make the exposure. Replace the plug and dark slide.
3. Now increase the film speed by 1/3 of a stop by closing down the iris. Repeat with plug #2. Do this until you've used 7 plugs. So, if you're testing 400 ISO film, this will give you exposures at 200, 250, 320, 400, 500, 600 and 800.
4. Going back to the original metered (zone V) exposure at EI 200, close down the iris (or change the exposure time) 3 stops. This will be a zone VIII exposure. Follow the above sequence again, closing down by 1/3 of a stop for each of the remaining squares.
5. Develop the negative as per the manufacturers instructions.
6. Using a densitometer, read the squares. Find the square in the first sequence that is 0.10 over film base+fog. This is your correct zone I exposure, and determines your EI.
7. Now look at the second set of squares, and find the one that has the same EI as the first set. Read this square.
If you're using a condenser enlarger, you want the net densitiy to be between 1.15, and 1.25. If you're using a diffusion enlarger, the range is 1.25 to 1.35. Alter your development time to get the densties somewhere in this range.
The cardboard cutout can be used for testing all your film/developer combinations, as well as n+/-? development times. It saves film, and times during the whole process.
This is pretty much the same sequence that Ansel Adams describes in his book The Negative; it's just a bit more frugal with film.
Hope that helps and LF photographers out there who want to do testing!
The same applies to roll-film users as well; you just don't need the cardboard cutout, plugs and dark slide :-)
-klm.